The Orocommerce B2B System manage static block by Content Blocks which are the foundation of your site and they can help create a custom layout. In Oro applications, you can modify the existing content blocks, or create your own. More info and how create manually plz follow this link :
https://oroinc.com/b2b-ecommerce/doc/current/user-guide/marketing-content-blocks 

So let’s imagine that you have create one content block , with unique alias ‘home-banner-top’ with any HTML content and restrictions , the question how you can render inside your theme by layout system .

Ok this banner well get showed in the home , the standard route for home page is oro_frontend_root So inside Resources/views/layouts/theme-name add folder  oro_frontend_root .

Note:  theme-name is your theme name or current default theme like blank.

Now inside folder  oro_frontend_root add banner.yml and fill with :
​

 
layout:
    actions:
        - '@setBlockTheme':
            themes: 'banner.html.twig'
        - '@addTree':
            items:
                home_banner_top:
                    blockType: content_block
                    prepend: true
                    options:
                        alias:  home-banner-top
            tree:
                page_content:
                    home_banner_top: ~
​

What’s means ? Is easy you have added new block which will get related to our content block already created manually from administration ‘home-banner-top’, the type of block is content_block , for more clean and structured YML we use  @addTree and placing our new content block directly inside  page_content . More info about layout system PLZ refer to our course:
https://www.ibnab.com/en/blog/orocommerce/orocommerce-layouts-system-mvsc  or to official docs https://oroinc.com/b2b-ecommerce/doc/current/dev-guide/front-ui/layouts 

And we added a file twig which is our renderer file for this block :
​

 
        - '@setBlockTheme':
            themes: 'banner.html.twig'
​

you should add file banner.html.twig inside folder oro_frontend_root and push this code:
​

 
{% block _home_banner_top_widget %}
  {{  block.vars.contentBlock.content | raw  }}
{% endblock %}
​

Is easy you’re using the id ‘home_banner_top ‘ of your block to define where you will render this snippet of code and we use {{  block.vars.contentBlock.content  }} to render the content of block.

Note: you can dump all variables of this block by using {{  block.vars.contentBlock  }} in developer mode

Now you have ability to render you HTML but let’s using other case when you  wanna use custom widget inside you content block and render it . Here you should render and compile in same time so your content twig is:
​

 
{% block _home_banner_top_widget %}
  {{  block.vars.contentBlock.content | render_content }}
{% endblock %}
​

the twig function render_content will compile and render you content not just simple raw of html . That is all .